ARM: 7103/1: plat-pxa: move PXA GPIO driver to GPIO subsystem

As per example from the other ARM boards, push the PXA
GPIO driver down to the GPIO subsystem so it can be consolidated.

Acked-by: Eric Miao <eric.y.miao@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>